[51.04] Near Infrared Spectroscopy of M2-9 and M1-92 - Two Young Bipolar Planetary Nebulae

We present high resolution near-infrared spectroscopy of two young bipolar planetary
nebulae M2-9 and M1-92. These longslit observations were made with the Cryogenic
Grating Spectrometer on the 2.1m telescope at KPNO. We detect H$_2$ emission from
both nebulae. We determine that this emission is radiatively excited in M2-9. Phillips et
al. (1985) detected the 2.122$\mu$m line of H$_2$ in M2-9 using a 12 arcsec beam and
speculated that this emission was confined to the central regions of the object. Using
our longslit data, we conclude that the H$_2$ emission is actually not present in the core
of the object, but rather is confined to the lobes of M2-9. We compare the spatial
distribution of the H$_2$ to that of Br$\gamma$ and optical lines.

We find that the H$_2$ emission in M1-92 is thermally excited. Previous work by
Trammell et al. (1993) showed that the optical spectrum of M1-92 is dominated by shock
emission produced in the lobes of the object. By comparing the optical line ratios to
published shock models, we determined the velocity of this shock to be 80-100 kms$^{-
1}$. We now compare our measured H$_2$ line ratios with published shock models to
estimate the shock velocity implied by the IR lines. By comparing the IR velocities to the
velocities indicated by the optical lines, we unify studies of the shocked material at
different wavelengths.

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This work was supported in part by NSF grant 91-15101.